The invention relates to vertical blinds of the type in which a plurality of support carriages are mounted for movement along a head-rail channel and slat carriers are mounted on each carriage for turning movement about an upright axis. The carriages are interconnected to control the spacing between the carriages when in an extended position along the head-rail channel, and traverse mechanism is connected to a lead one of the carriages for moving the carriages between an extended and a retracted position. In order to maintain a fixed space between the blind slats and a side of the window opening, it is common practice to lock or anchor a carriage at a trail end of the stack of carriages against movement along the head-rail during normal operation of the blind. However, there are occasions, such as when cleaning the window, when it is desirable to move the blind slats away from the side edge of the window. Arrangements have heretofore been made, for example as disclosed in U.S. Pat. No. 3,157,223, for releasably retaining a trail carriage of a vertical blind at a selected location along the head-rail. However, in some vertical blind installations, it is important to releasably retain the trail carriage at a fixed location relative to the end of the head-rail, in a manner that does not obstruct the space in the head-rail between the trail carriage and the blind operating mechanism at the end of the head-rail, so as to enable use of other devices such as a vertical blind track protector disclosed in U.S. Pat. No. 5,090,467.